Positioning devices are well known in the art, and are used across several technical domains. In the metrology domain, positioning devices are mostly found as rotary encoders, as in WO 2006107363 A1, or linear encoders as in U.S. Pat. No. 5,563,408. These encoders output one dimensional information about the position, and are operating with a resolution of the order of 1/10 of a micron or of a 1/10,000 of a degree. To reach a positioning with several degrees of freedom, these encoders can be part of a chain, for example in a robotic arm, with the disadvantage that the more encoders are used, the more the positioning resolution degrades. The state of the art of robotic arm positioning system has today a resolution, which reaches at best one micron.
In a different technical field, the document EP 0 390 648 A1 discloses a multidirectional contact sensor which comprises a mobile probe. The mobile probe is mounted on a rigid frame with the help of a flexible membrane. The rear part of the probe comprises a concave mirror which faces an optoelectronic system comprising optic fibres for detecting a movement of the probe. The concave mirror reflects a light beam emitted by the optoelectronic system toward a sensor which detects the intensity of the reflected light beam. The detected intensity depends on the orientation of the reflected light beam and though of the position of the probe. The reaching of different intensity levels is then used for the control of functions which depend on the position of the probe. Such a multidirectional contact sensor doesn't fit in a very small volume. Additionally, the accuracy of the detected positions lies between 0.2 and 0.4 microns which is not satisfactory for very small systems. Intensity fluctuations may also occur due to fluctuation in power supply, temperature variation, ageing of the light source, changes of mirror reflectivity, which impose limits in the stability and accuracy of the sensor.